I have set out utilize the idea of human
capital quite centrally, but assign a central role as well to what I have been
calling the external efects of human capital. Thls latter force is, it seems to
me, on a quite different footing from the idea of human capital generally: The
twenty years of research I have referred to earlier is almost exclusively
concerned with the internal effects of human capital, or with investments in
human capital the returns to which accrue to the individual (or his immediate
family). If it is this research that permits us to 'see' human capital, then the
external effects of this capital must be viewed as remaining largely invisible, or
visible at the aggregative level only.